The invention relates to a device for exhaust gas recycling in internal combustion engines equipped with a fuel injection system of the type revealed hereinafter. Control devices which are arranged to determine the composition of the operating mixture of an internal combustion engine and also control the exhaust gas recycling so that a certain air factor is attained, are already known. The recycling of quantities of exhaust gas adapted to the respective operating condition of the internal combustion engine represents an effective measure for reducing environmentally harmful components in the exhaust gas of an internal combustion engine. In particular, the proportion of nitrogen oxides in the exhaust gas can be reduced by the exhaust gas recycling feature. However, it is necessary to adjust and control the amount of exhaust gas fed to the internal combustion engine together with the quantity of fresh air supplied and together with the injected amount of fuel, for, with a thereby accomplished reduction of the nitrogen oxides in the exhaust gas, it is also possible to experience an increase in the soot, CO, and HC proportions.
The conventional control devices which ensure, with very low NO.sub.x emissions and with small HC emission, a long lifetime of the internal combustion engine are, however, in part very complicated and costly, since a large number of a great variety of control units, adjusting valves, servomotors, and the like is required.
Thus, a control device of a conventional type uses a hydraulic servomotor for controlling the throttle valve in the intake manifold, by means of which the amount of recycled exhaust gas can simultaneously be adjusted, since the throttle valve is positioned and constructed so that it operates, in its fully open position, simultaneously as a closing flap for the orifice of the exhaust gas recycling pipe. Accordingly, when the throttle valve is closed or almost closed, the inlet opening for the pipe which recycles the exhaust gases back to the intake manifold is fully open. The control of the throttle valve servomotor is effected via a valve in the controlled pressure chamber of a differential pressure valve, wherein the thus-controlled pressure chamber is connected with a metering cross section in the fuel supply line, regulated by a control slide valve. The position of the control slide valve is a function of a disk disposed in the intake manifold at right angles to the air flow direction. If the amount of fuel delivered by the injection pump is increased, a pressure increase occurs in the operating chamber of the servomotor via the differential pressure valve, and a corresponding opening of the throttle valve takes place until the state of equilibrium has been attained. There is the need for a simple, economical system, by means of which rather small vehicles can obtain sufficiently low exhaust gas emissions with less expenditure.